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|
module Issue.TypedValue
( Type (..),
cast,
castDef,
)
where
import Data.Maybe (fromMaybe)
import Data.Text (Text)
import Data.Text qualified as T
import Data.Time.Calendar (Day)
import Text.Read (readMaybe)
data Type a where
Date :: Type Day
Int :: Type Int
String :: Type Text
cast :: (forall a. Ord a => a -> a -> b) -> (Text -> Text -> Maybe b)
cast eq x y
| Just x' <- castTo Date x, Just y' <- castTo Date y = Just (eq x' y')
| Just _ <- castTo Date x, Nothing <- castTo Date y = Nothing
| Just x' <- castTo Int x, Just y' <- castTo Int y = Just (eq x' y')
| Just _ <- castTo Int x, Nothing <- castTo Int y = Nothing
| otherwise = Just (eq x y)
castDef :: b -> (forall a. Ord a => a -> a -> b) -> (Text -> Text -> b)
castDef def eq x y = fromMaybe def (cast eq x y)
castTo :: Type a -> Text -> Maybe a
castTo Date = readMaybe . T.unpack
castTo Int = readMaybe . T.unpack
castTo String = Just
|
